1. Field of the Invention
This invention relates generally to digital audio broadcast systems. More particularly, it relates to the inclusion and transmission of local information for each of a plurality of localities within a channel of a larger scale broadcast transmission.
2. Background of Related Art
Various methods of broadcasting signals are known. For instance, a number of attempts have been made to simultaneously broadcast similar copies of the same source material on different frequencies or channels, e.g., both in digital form, and/or one in digital form and one in analog form. This technique can be advantageously employed for non-commercial broadcasts such as cellular phone transmissions, e.g., to provide for backward compatibility and/or signal redundancy, as well as for commercial broadcasts such as digital television (DTV) or radio services such as FM.
For instance, FIG. 5 depicts a conventional method of simultaneously broadcasting two digital copies of the same source material along with an older standard analog waveform. In the shown example, the broadcast includes two digital audio broadcast signals A and B and one analog broadcast signal C transmitted in the same band on the same channel, otherwise known in the United States as an In-Band On-Channel (IBOC) Digital Audio Broadcast (DAB) or hybrid IBOC.
In the disclosed example, the hybrid IBOC DAB signal 600 includes a center band containing a first, analog copy of the source material, an upper band A containing a first digital copy of the same source material, and a lower band B containing a second digital copy of the same source material.
The use of both an analog broadcast signal C and digital broadcast signals A, B improves system reliability and/or backward compatibility by allowing the capability for both analog and digital receivers to receive and interpret at least one copy of the source material. In many cases, this provides backwards compatibility to analog systems as systems are replaced with more advanced digital counterpart systems. While FIG. 5 shows a single channel containing DAB information, FIG. 6 shows that both digital broadcast signals A and B (as well as analog broadcast signal C) are typically transmitted at the same time.
Many homes, offices and automobiles currently receive digital audio broadcast (DAB) information, which is broadcast by transmission to many receivers spread over a wide geographic region. Present terrestrial digital audio broadcast systems allow coverage over a finite distance from a broadcast transmitter, e.g., typically 10 to 70 miles from the broadcast transmitter. Thus, many broadcast transmitters are required to cover a large geographic area. In such systems, if the receiver is mobile, e.g., an automobile radio, the received signal will eventually fade out as the mobile receiver moves farther from the antenna of the broadcast transmitter, requiring the receiving party to retune their receiver to the broadcast frequency of another transmitter.
Such disadvantages can be overcome with the use of a wide area transmitter, e.g., a transponder located in a satellite in orbit around the earth. In this way, one or more satellites are able to provide fairly continuous coverage over a large scale area, e.g., over an entire nation. Similarly, another technique for transmitting digital audio broadcast information utilizes wired cable found in most homes can also overcome disadvantages of terrestrial radio frequency (RF) broadcasts. However, some disadvantages still remain and new disadvantages are caused in both satellite and cable digital audio broadcast systems.
For instance, there are often times in a digital audio broadcast system wherein it would be desirable or important to transmit local information relevant to persons in a particular locality. For instance, information such as local news, weather and/or traffic reports may be particularly relevant to persons in some localities and irrelevant and a even a nuisance if received by persons in other localities. Localized terrestrial wireless systems were able to accommodate this need to a certain extent because of the relatively small service area for any one transmitter. However, with the emergence and prevalence of satellite systems and cable systems, any one channel is broadcast throughout a very large geographic region containing a large number of localities.
FIG. 7A shows a conventional DAB transmitter for transmitting both local audio content and general broadcast audio content using separate channels of a transmission medium.
In particular, a signal based on the program content from a local audio content source 210 is provided to a first channel of a transmitter 814. The audio content is digitized if in analog form, and packetized and otherwise formatted for transmission by a module which packetizes and constructs header information 812, which is under the control of a controller 820. The formatting performed by the packetizer and header information module 812 includes functions of any appropriate protocol, e.g., a broadcast protocol such as simple time division multiplex framing protocols, or an unacknowledged UDP protocol commonly used for streaming media applications, to allow for proper transmission of program content signals to appropriate receivers in the broadcast area.
To transmit both general broadcast information and local broadcast information, the conventional DAB transmitter 814 utilizes separate channels. Thus, information from a general audio content source 800 is transmitted in a second channel of the transmitter 804. A packetizer and header information module 802 with respect to the general broadcast information properly formats that information for general broadcast to all receivers tuned to the general broadcast frequency. Unfortunately, in conventional systems, to receive a local content information source a receiver must tune to another channel dedicated throughout the general broadcast area to the transmission of local content information relevant only to a particular locality.
FIG. 7B shows a conventional DAB receiver for receiving either the local audio content or general broadcast audio content transmitted by the conventional DAB transmitter shown in FIG. 7A.
In FIG. 7B, the receiver is capable of tuning or selecting content information from either the general broadcast channel of a receiver 702 or from a local broadcast channel of the receiver 704. This tunability is functionally depicted as a switch 711 and controlled by a controller 706. The user of the receiver can inform the controller 706 as to which channel is desired, i.e., the general broadcast channel of the receiver 702 or any one of a large plurality of local broadcast channels of the receiver 704. The selected broadcast content information is properly assembled and prepared for playback in analog form by a broadcast information digital-to-analog converter 708, appropriately amplified by an audio player 710, and output on a speaker 712.
Unfortunately, in conventional DAB systems, the provision of both general broadcast information and local information for each of a large number of localities requires separate channels for each, i.e., a separate channel for each stream of local content information. This dedicated use of additional digital audio broadcast channels for the transmission of local information to all receivers, whether or not the receiver is in the locality to which the information pertains, is wasteful of bandwidth throughout the general broadcast area. Moreover, the provision of local information relevant to other localities as well as the one that the receiver is in may confuse a user outside of the intended locality. For instance, if a tornado warning is issued on a local weather broadcast intended only for a particular locality, but a receiver in another locality tunes into the dedicated channel carrying the local content information regarding the tornado, the user may not understand that the warning does not apply to their viewing or listening (i.e., reception) area.
There is thus a need for a digital audio broadcast method and apparatus which allows transmission of information relevant to particular locations without wasting valuable channels, and without the potential for causing confusion to users receiving local information intended for access by receivers in another locality.